1. Field of the Invention
The present invention relates to an organic light emitting display and a method of fabricating the same, and more particularly, to an organic light emitting display and a method of fabricating the same that are capable of reducing the total thickness of an organic layer by forming an optimal thickness of NaF layer between an emission layer and an opposite electrode of an organic light emitting display.
2. Description of the Related Art
In general, an organic light emitting display (OLED) is a self emissive display which electrically excites an organic compound to emit light. The OLED is classified into a passive matrix OLED and an active matrix OLED depending on a method of driving N×M pixels disposed in a matrix manner. The active matrix OLED has an advantage capable of easily realizing a high resolution and large-sized display, since the active matrix OLED has low power consumption in comparison with the passive matrix OLED. In addition, the OLED is classified into a top emission OLED, a bottom emission OLED, and a both-sides emission OLED having top and bottom emission directions, depending on an emission direction of light emitted from the organic compound. The top emission OLED has an advantage of a large aperture ratio, since the top emission OLED emits light in a reverse direction of a substrate, differently from the bottom emission OLED.
As the display device has been miniaturized and therefore low power consumption is required, an OLED including a main display window of a top emission OLED formed at one surface and a sub-display window of a bottom emission OLED formed at the other surface is widely used. The above-mentioned OLED is mainly used in a mobile phone, which includes a sub-display window formed at an exterior part and a main display window formed at an interior part. In case of a call waiting state of the mobile phone, a user can observe receiving sensitivity, battery residual capacity, time, and so on, through the auxiliary display window that consumes relatively low power.
FIG. 1 is a cross-sectional view of a conventional organic light emitting display.
First, a predetermined thickness of buffer layer 110 is formed on a transparent insulating substrate 100, and a thin film transistor including a polysilicon pattern 122, a gate electrode 132, and source and drain electrodes 150 and 152 is formed on the buffer layer 110. In this process, source and drain regions 120, into which impurities are injected, are disposed at both sides of the polysilicon pattern 122, and a gate insulating layer 130 is disposed on an entire surface including the polysilicon pattern 122.
Next, a predetermined thickness of passivation layer 160 is formed on the entire surface of the resultant structure, and the passivation layer 160 is etched by photolithography and etching processes to form a first via contact hole (not shown) for exposing one of the source and drain electrodes 150 and 152, for example, the drain electrode 152. The passivation layer 160 may be formed of a silicon oxide layer, a silicon nitride layer, or a stacked layer thereof.
A first insulating layer 170 is formed on the entire surface of the resultant structure. The first insulating layer 170 may be formed of one selected from a group consisting of polyimide, benzocyclobutene series resin, spin on glass (SOG), and acrylate, and functions to planarize an emission region.
Then, the first insulating layer 170 is etched by the photolithography and etching processes to form a second via contact hole (not shown) for exposing the first via contact hole.
Next, a pixel electrode 180 is formed through the second via contact hole to be connected to one of the source and drain electrodes 150 and 152, for example, the drain electrode 152. In this process, when the OLED is a top emission OLED, the pixel electrode 180 is formed of a reflective electrode, and when a bottom emission OLED, the pixel electrode 180 is formed of a transparent electrode. When the pixel electrode is the reflective electrode, the pixel electrode is formed in a stacked structure of the reflective electrode and the transparent electrode.
Next, a second insulating layer (not shown) is formed on the entire surface of the resultant structure. The second insulating layer may be formed of one selected from a group consisting of polyimide, benzocyclobutene series resin, phenol resin, and acrylate. Then, a second insulating layer pattern 190 for defining an emission region is formed by a photolithography process.
Then, an organic layer 182 including at least an emission layer is formed at the region defined by the second insulating layer pattern 190 through a small molecule deposition method or a laser induced thermal imaging method. The organic layer 182 may further include at least one layer selected from a group consisting of an electron injection layer, an electron transport layer, a hole blocking layer, a hole injection layer, and a hole transport layer.
Next, a predetermined thickness of LiF layer 184 is formed on the organic layer 182. At this time, the LiF layer 184 is an interface layer between the organic layer 182 and an opposite electrode 186, and has a thickness of about 3˜10 Å. The LiF layer 184 improves electron injection characteristics to decrease a work function of the opposite electrode 186, increase luminous efficiency, and lower a driving voltage.
Next, the opposite electrode 186 is formed on the LiF layer 184. The opposite electrode 186 is formed of a transparent metal electrode such as an Mg—Ag or Ca layer.
Then, a passivation layer (not shown) is formed on the opposite electrode 186. The passivation layer is formed of an inorganic insulating layer such as a silicon nitride layer.
However, in the conventional OLED, it is difficult to adapt an optimal thickness of organic layer between the pixel electrode and the opposite electrode in order to increase the luminous efficiency and decrease the driving voltage.